ch02

ch02/chainmap.py

@@ -0,0 +1,24 @@
+# chainmap.py
+
+
+>>> from collections import ChainMap
+>>> default_connection = {'host': 'localhost', 'port': 4567}
+>>> connection = {'port': 5678}
+>>> conn = ChainMap(connection, default_connection) # map creation
+>>> conn['port']  # port is found in the first dictionary
+5678
+>>> conn['host']  # host is fetched from the second dictionary
+'localhost'
+>>> conn.maps  # we can see the mapping objects
+[{'port': 5678}, {'host': 'localhost', 'port': 4567}]
+>>> conn['host'] = 'packtpub.com'  # let's add host
+>>> conn.maps
+[{'port': 5678, 'host': 'packtpub.com'},
+ {'host': 'localhost', 'port': 4567}]
+>>> del conn['port']  # let's remove the port information
+>>> conn.maps
+[{'host': 'packtpub.com'}, {'host': 'localhost', 'port': 4567}]
+>>> conn['port']  # now port is fetched from the second dictionary
+4567
+>>> dict(conn)  # easy to merge and convert to regular dictionary
+{'host': 'packtpub.com', 'port': 4567}